In any current device for enabling a metal organic chemical vapor deposition (MOCVD) process, the showerhead design can be the major factor affecting the flow field uniformity and deposition rate in the MOCVD process. In recent years, showerheads are arranged at position at the top of a process chamber and covering an area corresponding to a wafer carrier inside the process chamber. Thereby, the showerheads that are disposed above the wafer carrier are used for spraying a reaction gas to a wafer loaded on the wafer carrier.
In a MOCVD process for manufacturing light emitting diode (LED) epitaxial wafers, the flow field uniformity and residence time of the reaction gases that are being projected out of the showerheads are the key factors affecting the LED binning and production cost. That is, when the reaction gases inside the process chamber are distributed uniformly for a long period of residence time, not only the gas utilization ratio is improved, but also the MOCVD deposition rate is enhanced, and as a consequence, the power consumption and production cost are reduced.
For a film deposition process, the use of conventional showerheads for spraying reaction gases can generally cause a flow stagnation zone to happen in the center area of a process chamber due to overly concentrated distribution of reaction gases, and also the wavelength uniformity at wafer edge can be adversely affected. Consequently, a conventionally means for controlling the spraying of reaction gases into a process chamber while pumping the reaction gases to be exhausted out of the process chamber through a side of the process chamber is used for improving the flow field uniformity in the process chamber.
Nevertheless, although the flow field uniformity can be improved by the drawing of vacuum pump, the reaction gases are going to be drawn away from the wafer faster than it is intended in an ideal condition after the reaction gases is sprayed on the wafer. Thus, the residence time of the reaction gases inside the process chamber is shortened, and as a consequence, the utilization rate of the reaction gases is reduced and eventually the deposition rate is adversely affected. In addition, since the closer to the vacuum pump the reaction gases inside the process chamber will get more sparsely distributed, the wavelength uniformity at wafer edge can also be adversely affected.